
Eggshell
Common Idiom
The phrase 'walking on eggshells' means to be overly careful in handling a delicate situation. 
Literal and Figurative
'Eggshell' literally refers to the egg's outer layer, but it can also signify something extremely fragile. 
Collocation Caution
Collocations like 'peel an eggshell' are specific; 'peel a shell' would be incorrect. 